[use cases] add sql generator

[Undertone0809]

Description

Build a use case which can generate sql by prodiving db table.

An ideal situation, as in the example, would be to give the user an off-the-shelf sqlite database experience to generate sql.

Output

• A UI app is better
• A text input to pass the database source
• Some example to show how to use.
• Relevant doc(add into use case), readme, requirements.txt

What's more?

On this basis, you can build an application for chat to db table. Instead of generating sql, the Agent can further execute sql to query the information that the user wants to query.

Here is ref:

• https://python.langchain.com/v0.2/docs/integrations/toolkits/sql_database/
• https://python.langchain.com/v0.1/docs/use_cases/sql/quickstart/